1. Field of the Invention
The present invention relates to a stereoscopic image display technique. More specifically, the present invention relates to a stereoscopic image display device and the like for converting an image to a stereoscopic image with which an observer does not feel a sense of discomfort even when the observer changes one's position.
2. Description of the Related Art
Recently, television sets capable of viewing stereoscopic images are on the general market. Accordingly, the amount of the stereoscopic image contents is increased, and the environments for viewing the stereoscopic images are coming to be in good condition. In general, the observer wears eyeglasses for stereoscopic image display to project images of different parallaxes on left and right eyes so that the observer can view the stereoscopic image on the stereoscopic image television set. However, there are many observers who feel a sense of displeasure to wear the eyeglasses for stereoscopic image display, and a stereoscopic image display device that requires no such eyeglasses is desired. Further, when the eyeglass-type stereoscopic image display device is utilized as a mobile device, it is inconvenient since the stereoscopic image display device and the eyeglasses for stereoscopic image display are required to be carried to the outside. Thus, such stereoscopic image display device that requires no eyeglasses is more strongly desired for mobile use.
As the stereoscopic image display that requires no eyeglasses for stereoscopic image display, generally used is a type which divides spatial areas for projecting a stereoscopic image, and projects images of different parallaxes to each of the divided spatial areas so as to project images of different parallaxes to the left and right eyes of the observer. Through providing a lenticular lens and a parallax barrier on a stereoscopic display panel of the stereoscopic display device, the images of different parallaxes are provided for each of the divided spatial areas by separating the optically projected images.
With such-type of stereoscopic image display device using an optical light separating module such as a lenticular lens or a parallax barrier, it is not necessary to wear the eyeglasses for stereoscopic image display. Thus, it is excellent in terms of avoiding such trouble of wearing eyeglasses and is expected to be utilized in mobile use in particular. With the stereoscopic image display device which projects different images towards a plurality of viewpoints by using the optical light separating module, luminance unevenness (luminance fluctuation) occurs depending on the position of the stereoscopic display panel, and an image area that is displayed darker than peripheral image areas may appear when the observing position of the observer is shifted. This phenomenon is caused when a no display area (a light-shielding part referred to as black matrix in general in liquid crystal panel) between pixels of each viewpoint is visually recognized. The above-described phenomenon generated in accordance with shift of the observing position of the observer does not occur in a typical image display device having no optical light separating module. Thus, the observers may feel a sense of discomfort or deterioration of the image quality for such phenomenon occurred in the stereoscopic image display device having the optical light separating module.
This is the phenomenon referred to as “3D moiré” in general. 3D moiré is periodical luminance unevenness (also means color unevenness) caused when different images are projected to different angular directions. 3D moiré is luminance angular fluctuation, which may not be an issue depending on the observing position. However, when the luminance angular fluctuation is large, it is considered to give an undesired influence for stereoscopic image display. Therefore, it is desirable to make the luminance fluctuation equal to or smaller than a prescribed value.
In order to improve the issues caused due to the optical light separating module and the light-shielding part by the black matrix, various related techniques are proposed.
As a related technique, there is proposed a stereoscopic image display device with which the influence of the 3D moiré is lightened by moderating the luminance fluctuation caused by the 3D moiré by employing a structure in which the shape of pixels in a liquid crystal panel is formed in a substantially trapezoid form, the aperture part of sub-pixels is formed with a substantially trapezoid form having an upper base and a lower base substantially in parallel to the X-axis and two slopes tilted in directions different from the Y-axis direction, and a light-shielding part formed in a substantially triangular form is provided in an acute part of the substantially trapezoid form (Japanese Unexamined Patent Publication 2012-063556 (Patent Document 1)).
As another related technique, there is proposed a stereoscopic image display device with which the influence of the 3D moiré and the 3D crosstalk sensed by an observer is lightened by avoiding simultaneous generations of the image fluctuation effects of the both through shifting the image switching position and the positions where the 3D moiré and the 3D crosstalk appear by switching a left-eye image and a right-eye image not on a boundary line between a stereoscopic viewing space and a pseudoscopic viewing space but at a position nearer than that (Japanese Unexamined Patent Publication 2003-107392 (Patent Document 2)).
Further, with a stereoscopic image display device displaying images of multi-viewpoints, the luminance becomes higher in parallax images towards the center because of the viewing angle characteristic of a liquid crystal panel, the incident angle for the lens, and the lens aberration. Thus, luminance fluctuation is generated between the parallax image at the center and the parallax image at the edge. As a related technique for overcoming such issue, there is proposed a stereoscopic image display device with which the luminance fluctuation generated between the parallax image at the center and the parallax image at the edge is lightened through performing luminance adjustment processing which sets a range of brightness displayed on a pixel located in the center of element pixels which generate the parallax image to be smaller than a range of brightness of an image displayed on a pixel located on the boundary of the element pixels (Japanese Unexamined Patent Publication 2009-080144 (Patent Document 3)).
Further, with a stereoscopic image display device having an optical light separating module, a double image by the 3D crosstalk (3D crosstalk image, or, CT-image) appears depending on the observing position of the observer, thereby giving an undesired influence on stereoscopic image display. As a related technique for overcoming such issue, there is proposed a stereoscopic image display device with which the influence of a CT-image caused by the 3D crosstalk is lightened by measuring the observing position of the observer and performing luminance adjustment processing within sub-pixels which generate parallax images of multi-viewpoints according to the observing position (Juyong Park, et al, “Active Crosstalk Reduction on Multi-View Displays Using Eye Detection” SID2011, 61. 4, pp. 920-923 (Non-Patent Document 1)).
As another related technique, there is proposed a method which lightens the influence of a CT-image caused by the 3D crosstalk through converting one of the image data out of the image data of two viewpoints into a black image and projecting only the other image data at the observing position where the CT-image by the 3D crosstalk is projected (Japanese Unexamined Patent Publication 2008-089787 (Patent Document 4)).
Further, with a time-division stereoscopic image display device, luminance fluctuation occurs due to delay of a liquid crystal shutter. As a related technique for overcoming such issue, there is proposed a method which lightens the influence of the luminance fluctuation through adding black-side correction data or white-side correction data to the image area where the luminance value changes within the left-eye image (L image) and the right-eye image (R image) of a stereoscopic image content. Furthermore, also proposed is a method which lightens the influence of the CT-image caused by the 3D crosstalk through performing image blurring processing such as lowpass filter to the black-side image data and the white-side image data by adding gradual correction data so that the CT-image is hardly recognized by human eyes (Japanese Unexamined Patent Publication 2011-166744 (Patent Document 5)).
Further, with a parallax-barrier type stereoscopic image display device, luminance fluctuation occurs in a process of changing the transmittance characteristic of a barrier member by setting ON and OFF the electrodes. As a related technique for overcoming such issue, there is proposed a stereoscopic image display device with which the influence of the luminance fluctuation is lightened by adding a prescribed voltage (Japanese Unexamined Patent Publication 2011-018049 (Patent Document 6)).
Further, even when a stereoscopic image of a same parallax is displayed, the parallax of the stereoscopic image content observed by the observer changes depending on the distance between the stereoscopic image display device and the observing position of the observer. When the distance between the stereoscopic image display device and the observing position of the observer is too close, the parallax of the stereoscopic image content becomes too large and the stereoscopic image cannot be visually recognized. In order to overcome such issue, there is proposed a method for displaying a stereoscopic image by adjusting the parallax of the stereoscopic image content according to the distance between the stereoscopic image display device and the observing position of the observer (Japanese Unexamined Patent Publication 2012-044308 (Patent Document 7)).
Further, there is proposed a method which changes the barrier aperture position and the numerical aperture in the direction for increasing the number of viewpoints to adjust the luminance deterioration caused in accordance with the deterioration in the barrier numerical aperture generated in case of multi-viewpoints in order to widen the observing position of the observer with a parallax-barrier type stereoscopic image display device (Japanese Unexamined Patent Publication 2008-185629 (Patent Document 8)).
With the naked-eye stereoscopic image display device that requires no eyeglasses for stereoscopic image display, there is a large luminance fluctuation by the influence of 3D moiré depending on the observing position of the observer. This gives not only a sense of discomfort to the observer but also is one of the factors for causing physiological instability such as feeling video sickness and eye fatigue in a case of a stereoscopic image display device with a low picture quality, which is a reason for preventing the naked-eye stereoscopic image display device from being spread.
As a method for overcoming such issues, Patent Document 1 and the like are proposed. Patent Document 1 discloses a technique which lightens the luminance fluctuation caused by the influence of the 3D moiré with the shape of the pixels of the liquid crystal panel. However, with the technique of Patent Document 1, it is hard to lighten the influence of the luminance fluctuation by the 3D moiré in a case where slight 3D moiré is generated due to changes in the pixel shapes by the processing precision and manufacture variations and in a case where a liquid crystal panel having pixels in a shape other than that of the pixel shape used for a countermeasure for the 3D moiré is used.
Further, Patent Document 2 proposes a technique which lightens the influence of the 3D moiré and 3D crosstalk sensed by the observer by shifting the image switching position and the position where the 3D moiré and the 3D crosstalk appear. However, the technique of Patent Document 2 does not substantially lighten the influence of the luminance fluctuation by the 3D moiré even when the image switching position is shifted.
Further, Patent Document 3 proposes a technique which lightens the luminance fluctuation of parallax image of multi-viewpoints caused by the viewing angle characteristic of the liquid crystal panel, the incident angle for the lens, and the lens aberration by performing luminance adjustment of the element pixels which generate the parallax images. However, the technique of Patent Document 3 does not consider the method for lightening the luminance fluctuation caused by the 3D moiré generated from the black matrix of the liquid crystal panel and an optical light separating module such as a lenticular lens and does not perform luminance adjustment processing according to the observing position of the observer. Therefore, the influence of the luminance fluctuation caused by the 3D moiré cannot be lightened.
Furthermore, Non-Patent Document 1 proposes a technique which lightens the influence of a CT-image caused by the 3D crosstalk through measuring the observing position of the observer and performing luminance adjustment processing within sub-pixels which generate parallax images of multi-viewpoints according to the observing position. However, the technique of Non-Patent Document 1 does not consider the method for lightening the luminance fluctuation caused by the 3D moiré, so that the influence of the luminance fluctuation caused by the 3D moiré cannot be lightened.
Further, Patent Document 4 discloses a technique which lightens the influence of a CT-image caused by the 3D crosstalk through converting one of image data to a black image. However, the technique of Patent Document 4 has following issues. Since only the other image data is projected to the observer, the luminance value of the observed image projected to the observer is deteriorated, thereby causing the luminance fluctuation. As a countermeasure for the luminance fluctuation, it is depicted to increase the output of the backlight. However, the power consumption is increased, and the life of the backlight becomes shortened. Further, while the influence of the CT-image caused by the 3D crosstalk is taken into consideration therein, the influence of the luminance fluctuation by the 3D moiré is not taken into consideration. Therefore, the influence of the luminance fluctuation by the 3D moiré cannot be lightened.
Further, Patent Document 5 proposes a technique which lightens the influence of a CT-image caused by the 3D crosstalk through performing luminance adjustment processing by adding black-side correction data and white-side correction data for a time-division type stereoscopic image display device. However, the technique of Patent Document 5 does not perform the luminance adjustment processing by considering the observing position of the observer, so that it is not possible to lighten the influence of the luminance fluctuation which is caused by the 3D moiré when the observing position of the observer is shifted.
Patent Document 6 proposes a technique which lightens the luminance fluctuation through changing the transmittance of a barrier member by adding a prescribed voltage to the barrier member. However, the technique of Patent Document 6 has following issues: the cost of the stereoscopic image display device is increased since a device for applying the prescribed voltage is required; the technique can only be applied to a parallax-barrier type stereoscopic image display device; the influence of the luminance fluctuation by the 3D moiré cannot be lightened; etc.
Further, Patent Document 7 proposes a technique which performs parallax adjustment processing on a stereoscopic image content according to the distance between the stereoscopic image display device and the observing position of the observer. However, the technique of Patent Document 7 does not consider an image processing method for lightening the influence of the luminance fluctuation caused by the 3D moiré that appears in a naked-eye type stereoscopic image display device which projects a right-eye image and a left-eye image by spatially separating them with the use of a lenticular lens or a parallax barrier. Therefore, the influence of the luminance fluctuation caused by the 3D moiré cannot be lightened.
Further, Patent Document 8 discloses a method which adjusts the luminance deterioration caused in accordance with the decrease in the numerical aperture when the barrier aperture position is changed in the direction for increasing the number of viewpoints to have multi-viewpoints according to the observing position of the observer. However, the technique of Patent Document 8 has following issues: a method for lightening the luminance fluctuation of the 3D moiré generated from the black matrix of the liquid crystal panel and the optical light separating module such as a lenticular lens is not considered: the influence of the luminance fluctuation by the 3D moiré cannot be lightened with the luminance adjustment processing in accordance with the change in the barrier numerical aperture according to the observing position of the observer; etc.